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A250213
Number of distinct prime factors of A241601(n).
1
0, 0, 0, 0, 0, 0, 0, 1, 0, 1, 0, 2, 1, 2, 0, 2, 1, 1, 1, 3, 2, 2, 2, 3, 2, 2, 1, 2, 2, 4, 2, 2, 3, 3, 1, 3, 1, 3, 1, 1, 2, 3, 1, 3, 4, 5, 2, 2, 3, 1, 2, 4, 4, 4, 3, 4, 3, 5, 4, 2, 3, 3, 4, 5, 2, 3, 2, 4, 5, 5, 3, 3, 2, 5, 1, 5, 2, 4, 3, 2, 5, 3, 3, 2, 5, 3, 3, 4
OFFSET
0,12
COMMENTS
a(n) = 0 iff n is in the set {0, 1, 2, 3, 4, 5, 6, 8, 10, 14};
a(n) = 1 iff n is in A250220.
FORMULA
a(n) = A001221(A241601(n)).
MATHEMATICA
b[n_] := Numerator[BernoulliB[2 n]/(2 n)];
c[n_] := Numerator[SeriesCoefficient[Log[Tan[x]+1/Cos[x]], {x, 0, 2n+1}]];
a[0] = 0; a[n_] := PrimeNu[If[EvenQ[n], Abs[b[n/2]], c[(n-1)/2]]];
Table[a[n], {n, 0, 78}] (* Jean-François Alcover, Jul 04 2019 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Eric Chen, Dec 28 2014
EXTENSIONS
More terms from Jean-François Alcover, Jul 04 2019
More terms from Jinyuan Wang, Apr 02 2020
STATUS
approved